Recent interest in nucleic acids has generated a large body of experimental data concerning the conformation of these molecules in solution. Extensive x-ray optical, and nmr studies of model nucleosides and nucleotides have provided some details of the three-dimensional structures. The reasons behind the conformational behavior of these molecules, however, are not at once apparent. Thus, one objective of this research is to elucidate details of nucleic acid structure from semiempirical energy calculations and thereby to provide rational explanations of observed experimental phenomena. An initial problem of interest is to understand the unique structural roles of the different moieties comprising the nucleic acid repeat unit. A second objective is to use the calculated conformational energies in conjunction with statistical mechanical methods to predict certain properties of DNA and RNA polymers on the basis of their chemical structure. Finally, it is hoped that theoretical analyses of nucleic acid structure will anticipate problems of potential importance in experimental polynucleotide investigations.